The invention is a method of reading recorded data and a system employing this method. More specifically, the invention is a method and a system for reading magnetic tape, particularly a computer tape, containing several data tracks without knowing the exact position of the read heads relative to the tracks. Nonetheless, the invention is applicable to other types of recording.
A magnetic tape can form a high-density (1 .mu.m.sup.2 per bit on Evaporated Metal tape) data support. The physical formats used to record data on the tape can vary. The particular format depends on the performance required of the application and is closely tied to a specific type of recorder-playback machine.
In particular, there are three types of physical recording formats which depend on how the magnetic tape is scanned:
longitudinal recording PA1 transverse recording PA1 helical recording PA1 at least one set of individual magnetic heads are placed across the tape direction of travel, the number of individual heads exceeding the number of tracks on the tape; PA1 each individual magnetic head reads all magnetic data recorded on the tape passing in front of it; PA1 during a first integration operation, the absolute value of the signal output by each individual magnetic head is integrated for each individual magnetic head; PA1 a magnetic head, itself comprising at least one set of individual magnetic heads placed across the direction of travel of the tape, the number of individual magnetic heads exceeding the number of tracks on the tape; PA1 a first series of integration circuits to integrate the absolute values of the signals output by the individual magnetic heads, there being one integration circuit per individual magnetic head; PA1 a second series of integration circuits, there being one integration circuit common to each pair of neighboring individual magnetic heads, each circuit integrating the sum of the signals output by the two neighboring heads; PA1 a circuit to linearly combine the integration results from the first series of integration circuits and those from the second series of integration circuits.
In addition, neighboring tracks can be separate or adjacent and recorded at the same azimuth or different azimuths.
Finally, the organization of data within the tracks and the way they are represented on the tape (modulation mode) vary.
Consequently, existing recorders are generally only compatible with one recording standard or, at most, various standards differing only by the modulation mode used.
The most "natural" way of using magnetic heads is to allocate one read head to each physical track on the tape and then use a sufficiently accurate mechanical guidance system or a position servocontrol system to ensure each head is accurately positioned above the corresponding track.
However, this method is difficult to apply when several different recording formats are to be read with the same head or when it is necessary to read different tapes whose recording formats are not known. Moreover, there is a trend to use high recording densities on tapes and it then becomes necessary to ensure the magnetic head strictly follows the tracks on the tape; this is difficult to do.
The present invention overcomes these difficulties by offering a method and a magnetic tape read system which does not require the head to follow the tracks on the tape and which allows a tape to be read even if the position of the tracks (relative to the head positions) is unknown, i.e. when the recording format is not known.